Spontaneous firing explosive composition for use in a gas generator for an airbag

ABSTRACT

A spontaneous firing explosive composition for use in a gas generator for an airbag containing a fuel, an oxidizer, a combustion modifier, and a binder.

TECHNICAL FIELD

The present invention relates to a gas generating agent and a enhancerfor use in a gas generator to inflate an air bag for protection theoccupant in a vehicle and a gas generator using aforesaid gas generatingagent and enhancer. More specifically, this invention relates to anenhancer which has a spontaneous firing function and is safe-to-handle.And the enhancer is especially excellent in the properties required inthe ignition agent for gas generating agents and of which composition iscan also be used as gas generating agent itself. Further, this inventionrelates to a gas generator which is provided with an excellentspontaneous firing function to use aforesaid enhancer of whichcomposition can also be used as gas generating agents.

BACKGROUND OF THE INVENTION

As dissolved by U.S. Pat. No. 4,547,342 and FIG. 11, the gas generatorthat has been generally used, comprises a housing 1 with an uppercontainer body 2 and a lower container body 3. The upper container body2 has an inner cylinder wall 4 and an outer cylinder wall 6 with anintermediate cylinder wall 5 there-between and the lower container body3 has faces which are butted on the lower end portions of the cylinderwalls respectively and friction-welded so that the upper container body2 and the lower container body 3 may become into a unit. An ignitionchamber 7 is formed inside the inner cylinder wall 4 in the housing 1. Acombustion chamber G is formed between the inner cylinder wall 4 and theintermediate cylinder wall 5. A filter chamber F is formed between theintermediate cylinder wall 5 and the outer cylinder wall 6. And theinner cylinder wall 4 is provided with first gas holes 4 a, theintermediate cylinder wall 5 is provided with second gas holes 5 a andthe outer cylinder wall 6 is provided with gas release holes 6 a. In theignition chamber 7, an igniter 9 and enhancer 10 are placed. Inside thecombustion chamber G, gas generating agent 11 and a first filter 12 arearranged in the radial direction in that order. In the filter chamber F,a regulation plate 13 and second and third filters 14, 15 are mounted inthat order. The regulation plate 13 is bent at its upper end to contactwith the upper inner surface of the container 1 and seal the upperportion, and has a gas holes 13 a so that the gas from the combustionchamber G is led downward along the regulation plate 13 into the filterchamber F through the gas hole 13 a.

Upon crash of a motor vehicle, the sensor detects the impact and sendsan activate signal to an electric detonator taking a roll of an igniter9.

Then, the enhancer 10 is ignited by the flame from the igniter 9. Largequantity of heat particle current is generated by the enhancer 10 inturn flows into the combustion chamber G through the first gas holes 4 a(as indicated by an arrow in the drawing) and fires the gas generatingagent 11. The gas generating agent bursts out into flame thenhigh-temperature gas containing slug is produced. This gas cools downduring passing through the first filter 12, then flows into the filterchamber F through the second gas holes 5 a and goes downward along theregulation plate 13. The gas then passes through the gas holes 13 a andgoes upward along the second filter 14, and passes through the secondfilter 14 and the third filter 15 while the gas is cooled and cleared ofslug. Lastly, the gas becomes clear with a proper temperature and isdischarged into the air bag (not shown in the drawing) through the gasrelease hole 6 a.

The enhancer 10 used in the aforesaid gas generator takes a roll of acombustion improver to fire the gas generating agent 11, which isbasically different from the gas generating agent 11.

There is boron niter (BKNO₃) as one of the enhancers, which have beengenerally used. It is considered that a process of transfering fireproceeds as follows. The gasification percentage of boron niter is about10 percent. Therefore, when the igniter 9 ignites boron niter, theheated metal oxide particles are dispersed into the combustion chamber Gwith a generated heated gas current. Then, the heated metal oxideparticles stick on the surface of the gas generating agent 11. The gasgenerating agent 11 starts to burn at the struck spots. When the gasgenerating agent 11 is an organic type (so-called a non-azide type), thestuck spots, in other words, the heated areas of the gas generatingagent, are firstly softened and melted then vaporized. Consequently,combustion reaction are started at the stuck spots. Further, at theportions surrounding the the stuck spots, combustion reactions aresuccessively occurred by combustion heat from the the stuck spots in thesame manner. Thus, the combustion reaction broadens rapidly.

The combustion of the gas generating agent at an initial stage can beregarded as local combustions at the spots on which the heated boronparticles stick. Therefore, in order to increase the initial firing areaof the gas generating agent, it is suggested to assure making spaceamong of pellets of the gas generting agent so as to increase area onwhich the heated boron particles stick. The space among of the gasgenerating agent pellets plays a roll of a passage for the heated boronparticles passing through. However, according to this way, the packingpercentage of the gas generating agent pellets decreases and a largersize gas generator is required. This is contrary to the trend of sizeand weight reductions.

Also, when the packing density of the gas generating agent is raised soas to reduce size and weight of the gas generator, it is difficult forthe heated boron to stick to the pellets of the gas generating agentuniformly and it hard to adjust the combustion velocity.

Further, when a car which has met with no accident, is treated toabandon, the gas generator is remove from an air bag module andincinerated since it is difficult to pick up the only gas generatingagent from the air bag module. While the incineration of the gasgenerator, the housing of the gas generator is heated and becomes sobrittle. In this time, the gas generator may explode and break becauseof combution of the gas generating agent, which can bring danger to theneighboring area. Also, this kind of danger may occur in other case thanthe incineration, for example, when a car catches fire at accident otherthan a collision. Therefore, nowadays, such spontaneous firing explosiveas shown in U.S. Pat. No. 4,561,675 is proposed in order to preclude theabove danger. The spontaneous firing explosive is dispoed inside thehousing of the gas generator to separate from the gas generating agentand the enhancer, and is spontaneously fired before the housingdeterioration due to high temperature. In other words, the spontaneousfiring explosive is spontaneously fired at one temperature which islower than another temperature at which the housing deteriorates. Inplaced of the igniter 9, the spontaneous firing explosive ignites thegas generating agent in the gs generator. However, this method has aproblem that the fourth material like a spontaneous firing explosive isneeded in addition to the gas generating agent, the enhancer and theigniter. The gas generating agent, the enhancer and the spontaneousfiring explosive have different compositions respectively. Therefore, inorder to produce the prior gas generator, process and factory must beprovided to each of the gas generating agent, the enhancer and thespontaneous firing explosive although applied quantities of the enhancerand the spontaneous firing explosive are a very little in comparisonwith the gas generating agent. This is one of reasons of increasing acost for producing the gas generator.

The present invention aims to solve the above said problems involved inthe known gas generator including the above-mentioned known gasgenerating agent and enhancer. Specifically, the first aim of thepresent invention is providing enhancer having a function ofspontaneously firing at a temperature which is lower than anothertemperature at which the housing of the gas generator deteriorates. Thesecond aim of the present invention is provided an enhancer whichenables a gas generating agent, especially having an organic type fuelas main ingredient, to ignite uniformly. The third aim of the presentinvention is providing enhancer of which composition can be alsoemployed as a gas generating agent.

In other words, when an explosive composition having a function ofspontaneously firing at a temperature which is lower than anothertemperature at which the housing of the gas generator deteriorates, isemployed as an enhancer, further, when the spontaneous firing explosivecomposition is employed as a gas generating agent, it is not necessaryto provide with different facilities respectively for producing theenhancer, the spontaneous firing explosive composition and the gasgenerating agent. Whereby, an inexpensive gas generator can be provided.In these views, intensive research and development work have beenundertaken and resulted in the present invention which is disclosedhereinafter.

DISCLOSURE OF INVENTION

In order to achieve the aforesaid objects, the enhancer of the presentinvention is a mixture including a fuel ingredient, an oxidizing agentand a combution catalyst, which has a spontaneous firing function. Thefuel ingredient is a nitrogen atom-contained organic compound consistingof at least one kind selected from the group consisting ofazodicarbonamide, carbohydrazide, dicyandiamide, aminotetrazole,aminoguanidine, triaminoguanidine nitrate, nitroguanidine, triazole,tetrazole, azobitetrazole, bitetrazole, and salts of those compounds. Atleast 50% by weight of nitrate is contained as the oxidizing agent. Thecombustion catalyst contains substance selected from the followinggroups of {circle around (1)} to {circle around (3)}.

{circle around (1)} at least one kind selected from the group consistingof zirconium, hafnium, molybdenum, tungsten, manganese, nickel, iron andoxides and sulfides of those elements;

{circle around (2)} at least one kind selected from the group consistingof carbon and phosphorus; and

{circle around (3)} a mixture of the above members {circle around (1)}and {circle around (2)}.

The aforementioned fuel ingredient is a gas-generating ingredient whichburns and decomposes in order to produce gas. The oxidizing agent is aingredient for helping the fuel ingredient to burn. And the combustioncatalyst is a ingredient for adjusting the oxidizing reaction and thespontaneous firing temperature. By combining those ingredients, aspontaneous firing enhancer is produced with a high gasificationpercentage and good fuel-firing property.

As a binder for the particles of the enhancer mixture, it is desirableto employ at least one kind selected from the grops of {circle around(4)} to {circle around (7)}:

{circle around (4)} hydrotalcite-type compound expressed by thefollowing general formula:

[M²⁺ _(1−x)M³⁺ _(H)(OH)²]^(X+)[A^(n−) _(x/n).mH₂O]^(X−)

where

M²⁺ represents a bivalent metal such as Mg²⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺,Cu²⁺ and Zn²⁺;

M³⁺ represents a trivalent metal such as Al³⁺, Fe³⁺, Cr³⁺, Co³⁺ andIn³⁺;

A^(n−) represents an n-valence anion such as OH⁻, F⁻, Cl⁻, Br⁻, NO₃ ³¹ ,CO₃ ²⁻, SO₄ ²⁻, Fe(CN)₆ ³⁻, CH₃COO⁻, oxalate ion and salicylate ion; and

x: 0<x≦0.33.

{circle around (5)} Acid clay or activated clay

{circle around (6)} Natural zeolite or artificial zeolite

{circle around (7)} A mixture of two or more kind selected from thegroup consisting of the preceding {circle around (4)} to {circle around(6)}.

In the hydrotalcite-type compounds {circle around (4)}, hydrotalciteexpressed by a chemical formula Mg₆Al₂(OH₁₆CO₃.4H₂O or pyroauriteexpressed by a chemical formula of Mg₆Fe₂(OH)₁₆CO₃.4H₂O is the mostpreferable binders in consideration of all the factors including thebinding property, slug formation and commercial availability. It ispreferable that 2 to 30% by weight of the hydrotalcite-type compound isused in relation to the total weight of the enhancer, especially, 3 to10% by weight. It is preferable that a 50% average particle diameter ofa reference number is preferably set to be 30 μm or less.

The nitrates of alkali metals are preferable as the oxidizing agents.Preferably, the 50% average particle diameter of a reference numberfalls in the range of 5 to 80 μm.

The preferably quantity of the combustion catalyst is 10% by weight orless. The more preferable quantity falls in the range of 2% to 8% byweight. Preferably, the 50% average particle diameter of a referencenumber is 10 μm or less.

Furthermore, the enhancer of the present invention is granulated in apreferred embodiment. It is also preferable heat that the spontaneousfiring temperature of the enhancer falls in the rang of 150 to 180° C.in light of the gas generator having the aluminum housing.

The enhancer according to the present invention can be improved in agingcharacteristic or change of property with time when the granules of theenhancer are subjected to heat-treatment for 2 to 24 hours at 100 to120° C. after granulating. The granules treated by heat shows a goodstability during thermal aging resistance test for 400 hours at 107° C.It is noted that the heat-treatment is insufficient when theheat-treatment time is shorter than two hours. There is no differencebetween 24 hours and more in effect even when the heat-treatment time islonger than 24 hours. Therefore, heat-treatment time should be selectedfrom the range of 2 to 24 hours, more preferably 5 to 20 hours. Aneffect of the heat-treatment is a little when a temperature forheat-treatment is 100° C. or less. Also, an adverse effect may be givenwhen exceeding 120° C. On that ground, the temperature of heat-treatmentshould be selected from the range of 100 to 120° C., more preferablyfrom 105 and 115° C.

Further, the aforesaid enhancer composition can be used as the gasgenerating agent. When the binder as shown in {circle around(4)}-{circle around (7)} is employed, each pellet of the gas generatingagent has a high strength even though pellets are formed under a lowpelletizing pressure.

The gas generator of the present invention has a housing provided withoutlets for discharging gas, a gas generating agent, an igniter and anenhancer which is ignited by the igniter then fires the gas generatingagent. And further, the gas generator of the present invention appliesthe aforesaid enhancer composition to the enhancer and/or the gasgenerating agent. When an explosive composition is common to theenhancer and the gas generating agent, processes for producing anexplosive composition to be contained in the gas generator housing arerationalized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of the gas generator of the presentinvention;

FIG. 2 is a conceptional P-t diagram showing tank test results;

FIG. 3 is a table showing 40 cc-tank test results;

FIG. 4 is a schematic sectional view of another gas generator of thepresent invention used in Embodiment 2;

FIG. 5 is a table showing the reslts of 60-liter tank tests carried outin Embodiment 2 in which the condition of combustion was observed alongthe P-t curve;

FIG. 6 is a schematic sectional view of still another gas generator ofthe present invention used in Embodiment 3;

FIG. 7 is a table showing the results of 60-liter tank tests carried outin Embodiment 4;

FIG. 8 shows the testing apparatus used in a firing waiting time testperformed in Embodiment 5;

FIG. 9 is a table showing the result of a firing waiting time testconducted in Embodiment 5;

FIG. 10 is a table showing the results of a bon-fire test in Embodiment6; and

FIG. 11 is a schematic sectional view of the prior art gas generator.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will now be described in detailwith reference to the drawings and examples. FIG. 1 is a schematicsectional view of one gas generator of the present invention.

The gas generator shown in FIG. 1 is partitioned into an inner mostignition chamber A, an intermediate combustion chamber B and an outermost filter chamber by an inner cylinder wall a, an intermediatecylinder wall b and an outer cylinder wall c. An igniter 22 and anenhancer 23 are disposed in the ignition chamber A. The igniter 22sparks to be energized by the signal from a crash sensor (not shown inthe drawing) and the enhancer 23 is ignited by the igniter 22. A hightemperature gas generated by the combustion of the enhancer bursts intothe combstion chamber B through the first gas holes 24 a formed on theinner cylinder wall a then fires the gas generating agent 25 placedtherein. A gas produced by the combustion of the gas generatng agent 25bursts into the filter chamber C through the second holes 26 formed onthe intermediate cylinder wall b. In the filter chamber C, the slugcontained in the gas is removed from the gas and the gas is cooled bythe filter 27. The gas is discharged towards an airbag (not shown in thedrawing) through the third holes 28 formed on the outer cylinder wall c.

In the present invention, a mixture of ingredients selected from eachfollowing group (a)-(c), is employed as the explosive composition forthe enhancer. The one or more ingredients may be selected from the eachfollowing group (a)-(c). It is noted that this explosive compositionalso can be used as the gas generating agent.

(a) Fuel ingredient group consisting of azodicarbonamide,carbohydrazide, dicyandiamide, aminotetrazole, aminoguanidine,triaminguanidine nitrate, nitroguanidine, triazole, tetrazole,azobitetrazole, bitetrazole, and salts of those compounds, which areorganic compounds containing nitrogen atoms and produce gas includingnitrogen gas as a main ingredient to decompose by combustion.

(b) Oxidizing agent for burning the fuel ingredient; and

(c) Combustion catalyst for regulating the aforesaid oxidizing reaction.

Before mixing those explosive ingredients, it is desirable to adjust theparticle size of each ingredient. Preferably, a 50% average particlediameters of a reference number of the fuel ingredient and the oxidizingagent are set to be 5 to 80 μm respectively. It is preferable that a 50%averagle particle diamter of a reference number of the combustioncatalyst is 10 μm or less. When the 50% average particle diameters of areference number of the fuel ingredient and the oxidizing agent aresmaller than that, the two ingredients are so close each other that thespontaneous firing temperature tends to be set low, also, the combustionvelocity is so rapid that the gas generator may explode.

Further, when the 50% average particle diameters of a reference numberof the fuel ingredient and the oxidizing agent are larger than that, thecombustion velocity is so slow that the explosive ingredients may not beused as an enhancer. When the 50% average particle diameter of areference number of the combustion catalyst is larger than that, adispersion of the combustion catalyst among of the particles of fuelingredient and the oxidizing agent is insufficient and the function forregulating the combustion does not work enough.

It is noted here that the 50% average particle diameter of a referencenumber is measured on the basis of a distribution of the particlediameter. In the distribution, the total number of particles is set to100 and the numbers of particles corresponding to each particle diaemterare plotted. The particle diaemter at a reaching point in thedistribution of the particle diameter is regarded as the 50% averageparticle diameter of a reference number. The reaching point is the pointwhere the number of particles reaches 50 to be summed up from a side ofthe smaller particle diameter till reaching to 50 number of particles.

It is preferable that 50% or more by weight of nitrate is contained asan oxidizing agent. Whereby, a produced amount of NOx included in thegas can be reduced.

In the suitable nitrate group, there are alkali metal nitrates such aspotassium nitrate and sodium nitrate, alkaline earth metal nitrates suchas magnesium nitrate and strontium nitrate and ammonium nitrate.Especially, alkali metal nitrates are more preferable.

Next, ingredients selected from the following groups {circle around(1)}-{circle around (3)} are employed as the combustion catalyst.

{circle around (1)} At least one kind selected from the group consistingof zirconium, hafnium, molybdenum, tungsten, manganese, nickel, iron,their oxides and their sulfides,

{circle around (2)} At least one kind selected from the group consistingof carbon and phosphorus, and

{circle around (3)} A mixture of aforesaid members {circle around (1)}and {circle around (2)}.

The above combustion catalyst has functions for regulating the velocityof oxidizing reaction (combustion) between the aforesaid oxidizing agentand the fuel ingredient which is organic compound containing nitrogenatoms, and for regulating spontaneous firing temperature. When aspontaneous firing explosive composition including the above combustioncatalyst is employed as an enhancer, a spontaneous firing temperature ofthe enhancer can be adjusted so as to be spontaneously fired before thehousing of the gas generator deteriorates, in other words, thespontaneous firing temperature can be set to 200° C. or less, moresuitably, it can be set to 180° C. or less. And the gas generating agentis fired by the enhancer. Consequently, it is possible to prevent thehousing from exploding. In order to ensure the safety yielded from thespontaneous firing function, it is preferable to set the spontaneousfiring temperature between 150° C.-180° C. Whereby, it can be assuredthat the enhancer is fired then burns the gas generating agent beforethe aluminum housing of the gas generator deteriorates. Consequently,the safety of the gas generator can be secured. In the prior art, thegas generating agent is fired after a housing of the gas generatordeteriorats under the high temperature environment such as aconflagration. Consequently, the housing of the gas generator explodesbecause of the burning gas generating agent. On the contrary, there isno problem such as the above in the present invention. The safety of thegas generator can be more secured in case of the emergency such as aconflagration.

It is preferable that the quantity of the combustion catalyst is set to10% or less in relation to the total weight of the explosive compositionso that an amount of the gas yield from the explosive composition maynot be reduced and so that a large amount of the combustion slug may notbe yield.

Since organic compounds are employed as fuel ingredinets in the enhancerof the present invention, a ratio of yielding the gas is about 55% whichis larger than a prior art. For example, in one of the prior art, boronniter is employed as a fuel ingredient and a ratio of yielding the gasis about 10%. Therefore, the mechanism of firing the gas generatingagent by this enhancer is basically different from that of the boronniter in which the gas generating agent is fired by heat particles. Inthe present invention, the enhancer generates a large quantity ofhigh-temperature heat gas (presumably as high as 2,000° C.) which burstsinto the combustion chamber a through the first holes 24 formed on theinner cylinder wall and covers all the surfaces of the gas generatingagent pellets 25 in the combustion chamber. That triggers the processesof softening, melting, gasification and combustion reaction over the allsurfaces of the gas generating agent pellets 25 almost simultaneously.Therefore, even when the packing density of the gas generating agent ishigh and passages of the firing energy (heat particles or heat gas) floware narrow, as osmosis of the heat gas can be sufficient. When the gasgeneratng agent is packed to a high density, size and weight reductionsof the gas generator can be achieved.

Next, when aforesaid explosive composition is applied to the enhancer,it is prferable that the explosive composition is granulated and theparticle diameter is 1 mm or less. When aforesaid explosive compositionis applied to the gas generating agent, it is preferable that theexplosive composition is formed into one disk or a plurality of pelletshaving appropriate shapes and appropriate sizes. In the presentinvention, it is preferable that the explosive composition is formedwith at least one binder selected from the following groups {circlearound (4)}-{circle around (7)} in order to obtain a high-strength:

{circle around (4)} hydrotalcite-type compounds expressed by thefollowing general formula:

[M²⁺ _(1−x)M^(s+) _(x)(OH)₂]^(X+)[A^(n−) _(x/n)·mH₂O]^(x−)

where

M²⁺ represents a bivalent metal such as Mg²⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺,Cu²⁺ and Zn²⁺;

M^(s+) represents a trivalent metal such as Al³⁺, Fe^(s+), Cr³⁺, andIn³⁺;

A^(n−) represents an n-valence anion such as Oh⁻, F⁻, Cl⁻, Br⁻, CO₃ ²⁻,SO₄ ²⁻, Fe(CN)₆ ³⁻, CH₃COO⁻, oxalate ion and salicylate ion; and

x: 0<x≦0.33.

{circle around (5)} Acid clay or activated clay

{circle around (6)} Natural zeolite or artificial zeolite

{circle around (7)} A mixture of two or more selected from the groupconsisting of the preceding {circle around (4)} to {circle around (6)}.

In the hydrotalcite-type compounds {circle around (4)}, hydrotalciteexpressed by a chemical formula Mg₆Al₂(OH₁₆CO₃.4H₂O or pyroauriteexpressed by a chemical formula of Mg₆Fe₂(OH)₁₆CO₃·4H₂O is the mostpreferable binders in consideration of all the factors including abinding property, a slug formation and a commercial availability.

These binders offer another advantage as follows. When the explosivecomposition with the above binders burns, the harmful fine particlesproduced by combustion, react with the metal oxides produced by thedecomposition reaction of the binders, then slugs are formed. The slugsare easily removed by the filter.

These binders are contained by 2-30% by weight in relation to the totalexplosive composition. When an amount of the binders is less than 2% byweight, a binder function can not work. When the amount of the bindersexceeds 30% by weight, an amount of other ingredients is reduced then anexplosive function can not work. Therefore, it is preferable that 3-10%by weight of the binder is added.

The particle size of these binders is one of the important factors inthe production technique. It is preferable that a 50% average particlediameter of a reference number is 30 μm or less in the presentinvention. When the particle diameter degree is larger than that, afunction for binding each ingredients is reduced then a binding effectis a little. Therefore, a required strength concerning the formationbody of the explosive composition can not obtained.

Further, in case of producing an enhancer employing the above explosivecomposition, ingredients selected from each aforesaid group such as thefuel ingredient (a), the oxidizing agent (b), the combustion catalyst(c) and the aforesaid binder are mixed after each ingredient ispulverized into particles having required particle diameters asdescribed above. In case of necessity, organic or inorganic additive isfurther added. The mixture is granulated. It is preferable that the eachgranule diameter falls in a range of 0.3 to 1.00 mm since it isnecessary that a burning velocity of the enhancer is more rapid than oneof the gas generating agent. It is preferable that granules of theenhancer undergo such a heat treatment as has been described above.

Also, in case of producing a gas generating agent employing the aboveexplosive composition, ingredients are mixed after pulverizing asdescribed in case of the enhancer. The mixture is charged in a mold soas to be formed into a suitable shape by an ordinal press-forming. Nolimit is placed on a formable shape and size. In case of formed intopellets, the pellets can take various shapes and sizes. For example, alow height cylindrical shape, a sphere, an intermediate shape betweenthe sphere and the low height cylindrical shape. When a low heightcylindrical shape is employed, it is preferable that its diameter fallsin a range of 5 to 8 mm and its thickness falls in a range of 2 to 4 mm.Also, it is possible to be formed into one disc of which diameter andthickness may be settled according to the size of the gas generator.

The formed body of the gas generating agent is subjected to a heattreatment for 2 to 24 hours at 100 to 120° C. after the forming process.And the resistance to change with time can be enhance. The formed bodythus heat-treated shows a high degree of stability in a vigorous thermalaging resistance test for 400 hours at 107° C. It is noted that the heattreatment is insufficient when heat treatment time is shorter than twohours and there is not significant difference in an effect between under24 hours and over even though the heat treatment time exceeds 24 hours.Therefore, the heat treatment time should be settled between 2 and 24hours, more preferably 5 and 20 hours. In addition, there is littleeffect when a heat treatment temperature is 100° C. or less and adeterioration may occur when the heat treatment temperature exceeds over100° C. On that ground, it is preferable that the temperature of heattreatment falls in a range of 100 to 120° C., more preferably 105-115°C.

Now, the present invention will be described concretely in embodiments.

[EMBODIMENT 1]

34.2% by weight of 5-amino-1H-tetrazol (5-ATZ) was prepared as the fuelingredient to be pulverized into particles of which each diameter was100 μm or less and a 50% average particle diameter of a reference numberwas 30 μm. 56.8% by weight of potassium nitrate was prepared as theoxidizing agent to be pulverized into particles of which each diameterwas 100 μm or less and a 50% average particle diameter of a referencenumber was 55 μm. 4.5% by weight of MoO₃ was prepared as the combustioncatalyst to be pulverized into particles of which each diameter was 30μm or less and a 50% average particle diameter of a reference number was2 μm. 4.5% by weight of synthetic hydrotalcite was prepared as thebinder to be pulverized into particles of which each diameter was 50 μmor less and a 50% average particle diameter of a reference number was 10μm. These ingredients were mixed well in a V-shaped mixer. The powderedmixture was stirred while spraying with water then formed into granulesof which diameter is 0.5 mm. Thus an enhancer of the present inventionwas made. 1 [g] of the enhancer of the present invention and 1 [g] ofthe enhancer of the prior art were subject to a 40-cc tank test.

This test was one for examining the power of the enhancer. 1 [g] of theenhancer is placed in the 40 cc-tank. The change concerning an internalpressure P of the tank is measured with time after ignition of theenhancer by a squib. A P-t diagram as shown in FIG. 2 is obtained. InFIG. 2, t₀ indicates the time of ignition by squib, t₁ indicates thetime when the internal pressure reaches to a peak P_(m), t_(m) is therequired time (t₁−t₀) for reaching to peak internal pressure P_(m) fromthe time t₀. The results of the 40-cc tank test is summarized in FIG. 3.The exothermic values given in FIG. 3 were measured using a calorimeter.

As shown in FIG. 3, the enhancer of the present invention shows a highpower (maximum pressure) even though exothermic value is low as comparedwith the conventional enhancer. This probable reason is that thegasification ratio in the prior art is 10% which is low, on the contrarythe gasification ratio in the present invention is 55% which is high.Therefore, the enhancer of the present invention generates a largeamount of high-temperature heat air. The heat air flows into the gasgenerating agent-packed portion quickly and fires the gas generatingagent simultaneously.

There will now be described another embodiment in which an explosivecomposition is common to the enhancer and the gas generating agent.

[EMBODIMENT 2]

The construction of the gas generator used in the embodiment 2 isillustrated in FIG. 4. In FIG. 4, the reference number 30 indicates acombustion chamber containing pellets of the gas generating agent 36.The reference number 32 shows a firing means mounted in the center ofthe combustion chamber 30, which comprises a squib 34 and a enhancer 35for firing the gas generating agent 36.

The reference number 33 is a filter chamber surrounding the combustionchamber annularly, which cools the gas passing through the combustionchamber 30 and collects the slug from the gas. Sparks from the squib 34melt a container 40 b made of aluminum foil then the enhancer 35ignites. A high-temperature gas generated during the combustion of theenhancer bursts into the combustion chamber 30 to melt a container 41made of aluminum foil for the gas generating agent in the combustionchamber 30 then fires the gas generating agent 36 in the combustionchamber 30. The gas produced during the combustion of the gas generatingagent flows into the filter chamber 33 through first gas outlets 39 cformed on the partition wall 39. In the filter chamber 33, the slug isremoved from the produced gas while the produced gas is cooled. Afterthat, the cooled gas is discharged from the second holes 38 c providedon the outer wall 38 into an air bag (not shown in the figure).

The enhancer 35 and the gas generating agent 36 were made of the sameexplosive composition by the following manner.

(One explosive composition)

34.2% by weight of 5-amino-1H-tetrazol (5-ATZ) was prepared as the fuelingredient to be pulverized into particles of which each diameter was100 μm or less and a 50% average particle diameter of a reference numberwas 30 μm. 56.8% by weight of potassium nitrate was prepared as theoxidizing agent to be pulverized into particles of which each diameterwas 100 μm or less and a 50% average particle diameter of a referencenumber was 55 μm. 4.5% by weight of MoO₃ was prepared as the combustioncatalyst to be pulverized into particles of which each diameter was 30μm or less and a 50% average particle diameter of a reference number was2 μm. 4.5% by weight of synthetic hydrotalcite was prepared as thebinder to be pulverized into particles of which each diameter was 50 μmor less and a 50% average particle diameter of a reference number was 10μm. These ingredients were mixed well in a V-shaped mixer. In order toobtain pellets of the gas generating agent, one piece of the mixture wasfilled into a reference mold then press-formed into the pellets. Eachpellet shape had a low height cylindrical shape of which diameter was 7mm, thickness was 4 mm and weight was about 250 mg. In order to obtaingranules of the enhancer, other piece of the mixture was granulated.Each granule had a diameter of 0.5 mm.

(Other explosive composition)

Separately, other enhancer and other gas generating agent were preparedin the following process. 42.3% by weight of 5-amino tetrazole potassiumsalt (K-5ATZ) was prepared as the fuel ingredient to be pulverized intoparticles of which each diameter was 100 μm or less and a 50% averageparticle diameter of a reference number was 30 μm. 48.7% by weight ofpotassium nitrate was prepared as the oxidizing agent to be pulverizedinto particles of which each diameter was 100 μm or less and a 50%average particle diameter of a reference number was 50 μm. 4.5% byweight of Fe₂O₃ was prepared as the combustion catalyst to be pulverizedinto particles of which each diameter was 30 μm or less and a 50%average particle diameter of a reference number was 2 μm. 4.5% by weightof acid clay was prepared as the binder to be pulverized into particlesof which each diameter was 50 μm or less and a 50% average particlediameter of a reference number was 10 μm. These ingredients were mixedwell in a V-shaped mixer. In order to obtain pellets of the gasgenerating agent, one piece of the mixture was filled into a referencemold then press-formed into the pellets. Each pellet shape had a lowheight cylindrical shape of which diameter was 7 mm, thickness was 4 mmand weight was about 250 mg. In order to obtain granules of theenhancer, other piece of the mixture was granulated. Each granule had adiameter of 0.5 mm.

The enhancer and the gas generating agent which had the same explosivecomposition each other, were packed in the gas generator as shown inFIG. 4. The gas generator packed with the enhancer and the gasgenerating agent was subject to the 60-liter tank test in order toexamine the ability of the gas generator. The 60-liter tank had beenconstructed so that the inside temperature could be raised up to about250° C. And two kind of the gas generators had been built to each kindof aforementioned explosive composition, one was provided with the firstgas outlets 39 c having a total opening area of 200 mm² and the otherwas provided with the first gas outlets 39 c having a total opening areaof 400 mm². In the 60-liter tank test, the above-mentioned gasgenerators were mounted in the hermetical closed 60-liter tanksrespectively then activated. And the change concerning an internalpressure P of the each tank was measured with time t, from which a P-tdiagram as shown in FIG. 2 was obtained as well as [EMBODIMENT 1]. Inthis case, t₀ indicates the time when the gas generator startsactivation, t₁ indicates the time when the internal pressure reaches toa peak P_(m), t_(m) is the required time (t₁−t₀) for reaching to thepeak internal pressure P_(m) from the time t₀. In the P-t diagram, acombustion velocity is rapid when a curve indicating the pressure Prises sharply, and the gas generator may explode when the maximumpressure P_(m) is too high. Also, when t_(m) is too long, it takes longtime to inflate the air bag. The air bag must be instantaneouslyinflated, therefore the explosive composition having too long t_(m) isnot suitable for the gas generating agent for inflating the air bag.Even though the desired values of P_(m) and t_(m) depend on the size,the arranged position, the use of air bags (for the driver, for thepassenger, for a side crash accident, or the like) and the car model(passenger car, bus, truck or other vehicles), it is desirable thatP_(m) falls in the range of 150 to 250 kPa and t_(m) is 150 ms or less.

In the 60-liter tank test, the combustion condition was examined as wellas the P-t curve. The test results are shown in FIG. 5.

As shown in FIG. 5, the attained maximum pressures P_(m) wereappropriately high and the required times t_(m) for reaching the maximumpressures P_(m) were appropriately short in all the tests. These showthat the combustions have gone on safely and smoothly. From the resultof the 60-liter tank test, it is realized that the enhancer of thepresent invention fires the gas generating agent extremely smoothly.

[EMBODIMENT 3]

An embodiment of a gas generator having the construction illustrated inFIG. 6 will now be described. This gas generator in FIG. 6 has structualdifferences from the gas generator in FIG. 4 as follows. In FIG. 6, anintegral-type igniter 32 is employed in which an enhancer 35 isincorporated in the igniter 32. The annular aluminum foil container 41has a portion which can communicate in the radial direction at its upperside, which is disposed in an annular combustion chamber 30 formed inthe space between the igniter 32 and a partition wall 39. The gasgenerating agent 36 is contained in the container 41. An explosivecomposition employed as an enhancer and a gas generating agent is thesame one as employed in the embodiment 2. Combustion tests using the gasgenerator of Embodiment 3 were done in the same manner as Embodiment 2.Satisfactory results were obtained as well as in Embodiment 2.Especially, in Embodiment 3, a holder for the enhancer as shown in theprior art is not necessary. The construction of the gas generator can besimplified by this reduction concerning the number of the parts. Thiswill help to reduce a cost of production.

[EMBODIMENT 4]

A case in which explosive compositions of the enhancer and the gasgenerating agent are different from each other, will be describedhereinafter.

36.2% by weight of 5-amino-1H-tetrazol (5-ATZ) was prepared as the fuelingredient to be pulverized into particles of which each diameter was100 μm or less and a 50% average particle diameter of a reference numberwas 30 μm. 59.3% by weight of strontium nitrate was prepared as theoxidizing agent to be pulverized into particles of which each diameterwas 100 μm or less and a 50% average particle diameter of a referencenumber was 45 μm. 4.5% by weight of synthetic hydrotalcite was preparedas the binder to be pulverized into particles of which each diameter was50 μm or less and a 50% average particle diameter of a reference numberwas 10 μm. These ingredients were mixed well in a V-shaped mixer. Inorder to obtain pellets of the gas generating agent, the mixture wasfilled into a reference mold then press-formed into the pellets. Eachpellet shape had a low height cylindrical shape of which diameter was 7mm, thickness was 4 mm and weight was about 250 mg. This gas generatingagent has no spontaneous firing function since no combustion catalyst iscontained.

Then, the same enhancer as is prepared in Embodiment 1 and the gasgenerating agent obtained as above were loaded in a gas generatorillustrated in FIG. 4. The gas generator underwent the same 60-litertank test as in Embodiment 2. The test results are given in FIG. 7.

As clearly understood from FIG. 7, the present invention gave good gasgenerator characteristics in combination with another organic type ofgas generating agent having no spontaneous firing function.

[EMBODIMENT 5]

Firing waiting tests as follows, were carried out in order to examinethe spontaneous firing functions of the explosive compositions.

As shown in FIG. 8, an oil bath 51 with an automatic temperature controlwas filled with silicone oil 54 and was provided with an iron cylinder50 of which an inside diameter is 2 cm and a length is 20 cm. Thetemperature was maintained at 182.5±2.5° C. by a heater 52 and athermometer 53. Then 0.1±0.01 [g] of the explosive composition wasplaced in the iron cylinder 50. And the required time to bespontaneously fired or to make spontaneous firing sound was measured.When the spontaneous fire or the spontaneous firing sound of anexplosive composition was measured within 3 minutes, it was estimatedthat the explosive composition had a spontaneous firing function. Eachexplosive composition was tested three times. The test results aresummarized in FIG. 9.

As clearly understood from FIG. 9, the explosive compositions of thepresent invention was fired at about 180° C. within 3 minutes. BKNO₃ ofthe prior art and the explosive composition containing no combustioncatalyst were not fired. The firing waiting times of the test No. 02(MoO₃ used) and the test No. 04 (Fe₂O₃ used) were different form eachother since spontaneous firing temperatures depended on various kind ofcombustion catalyst.

[EMBODIMENT 6]

The enhancer of the present invention and the gas generating agent wereloaded in a gas generator as illustrated in FIG. 4. The gas generatorunderwent a bonfire test in order to examine the spontaneous firingfunction of the gas generator. The required time for firing the gasgenerator was measured. When the gas generator was fired within threeminutes with no damage on the housing of the gas generator, it wasestimated that the gas generator had a spontaneous firing function. Thetest results are shown in FIG. 10. Other enhancers and gas generatingagents made of other explosive compositions than the present inventionalso underwent the test as the comparisons.

As clearly understood from FIG. 10, it was estimated that the gasgenerators of the present invention had spontaneous firing functionssince they were fired within three minutes without no damage on thehousings of them. The other hands, other enhancers and gas generatingagents made of other explosive compositions than the present inventionwere fired with more than three minutes and with damages on the housingsof them. This means that other explosive compositions than the presentinvention need additional ingredients having spontaneous firing functionfor preventing housings of their gas generator from damaging.

As described above, according to the enhancer of the present inventionincluding the nitrogen atoms-contained organic compounds as fuelingredients, the gas generating agent is simultaneously fired even whena packing density of the gas generating agent is high. Because a heatgas is generated during a combustion of the enhancer and permeates amongof the pellets of the gas generating agent then the gas generating agentis simultaneously fired. This is different from the prior art of firingwith heat particles of boron niter. Consequently, the packing densityconcerning the pellets of the gas generating agent becomes higher thanone of the prior art and the reductions concerning a size and a weightof the gas generator can be achieved.

In case of the gas generating agent including the nitrogenatoms-contained organic compounds, the gas generating agent burnsthrough the processes of softening, melting, vaporization and reaction(combustion). In the present invention, heat required to the processescan be continuously supplied from the surroundings since the processesof softening, melting, vaporization proceed under a heat gaseousatmosphere, which are endothermic processes. Therefore, these processesproceed without interruption and the gas generating agent is fired andburns smoothly. From these views, we can say that the enhancer of thepresent invention possesses the most suitable characteristics ofigniting the gas generating agent of the organic type.

Further, according to the present invention, the quantity of solidproducts produced from the enhancer is less and the exothermic value islower than the prior art. The exothermic value of the present inventionis 3.4 kJ/g while one of the prior art including boron niter is 4.6kJ/g. Furthermore, the gas bursting into the air bag is clean since thepresent invention uses such binders as hydrotalcite-type compoundsyielding the slugs which are easily collected.

Also, according to the present invention, in emergencies like aconfiguration, the enhancer is spontaneously fired then ignites the gasgenerating agent before the deterioration of the gas generator housingsince the enhancer of the present invention has a function of beingspontaneously fired at the temperature of 180° C. or less which is lowerthan the heat deterioration temperature of the aluminum housing.Therefore, it is possible to prevent the housing from exploding.Consequently, in the present invention, it is not necessary thatadditional explosive composition which has a spontaneous firing functionis arranged in the gas generator, and the construction of the gasgenerator can be simplified in comparison with the prior art.

Still another advantage is that the enhancer of the present inventioncan be easily and safely handled since there is little fear of theenhancer ignited by impact in comparison with the prior art of boronniter.

It is further noted that the enhancer composition of the presentinvention can be also used as a gas generating agent. Therefore, whenthe enhancer composition of the present invention is employed as boththe enhancer and the gas generating agent, processes for producing thethe enhancer and the gas generating agent become common to them. Thisenables the processes for producing explosive compositions to be mountedin the gas generator to to be simplified and enables the product cost tobe reduced.

Also, according to the present invention explosive composition, a ratioof yielding the gas is about 55% which is larger than a prior art.Therefore, when the explosive composition of the present invention isemployed as a gas generating agent, a quantity of the gas generatingagent can be reduced and reductions concerning size and wight of the gasgenerator can be brought.

INDUSTRIAL APPLICABILITY

The enhancer of the present is suitable as a enhancer for use in a gasgenerator to inflate an air bag for protecting the occupant in avehicle. Specifically, the enhancer of the present is suitable as aenhancer having a function of spontaneously firing at a temperaturewhich is lower than another temperature at which the housing of the gasgenerator deteriorates. Further, the enhancer of the present is suitableas a enhancer which enables a gas generating agent, especially having anorganic type fuel as main ingredient, to ignite uniformly.

The gas generator of the present invention is suitable as a gasgenerator able to be inexpensively produced. Because the gas generatorof the present invention employs the above enhancer composition, havingthe spontaneous firing function, as both the enhancer and the gasgenerator, consequently, there is no necessity of providing withdifferent facilities respectively for producing the enhancer, thespontaneous firing explosive composition and the gas generating agent.

What is claimed is:
 1. A spontaneous firing explosive composition foruse in a gas generator for an air bag, comprising: a fuel, an oxidizer,a combustion modifier and 2-30% by weight of a binder, wherein saidbinder has 30 μm or less of a 50% average particle diameter of areference number and the above agents are mixed, and said fuel is atleast one nitrogen atom-containing organic compound selected from thegroup consisting of azodicarbonamide, carbohydrazide, dicyandiamide,aminotetrazole, aminoguanidine, triaminoguanidine nitrate,nitroguanidine, triazole, tetrazole, azobitetrazole, bitetrazole, andsalts thereof, said oxidizer contains at least 50% by weight ofpotassium nitrate, said combustion modifier is selected from thefollowing groups (1)-(3): (1) at least one member selected from thegroup consisting of zirconium, hafnium, molybdenum, tungsten, manganese,nickel, iron and oxides and sulfides of those members, (2) at least onemember selected from the group consisting of carbon and phosphorus, and(3) a mixture of the above members (1) and (2), said binder, which bindssaid fuel, oxidizer and combustion modifier, is at least one memberselected from the following groups i)-iv): i) hydrotalcite-type compoundhaving the formula: [M²⁺ _(1−x)M³⁺ _(x)(OH)₂]^(x+)[A^(n−)_(x/n)·mH₂O]^(x−) where M²⁺ is a bivalent metal selected from the groupconsisting of Mg²⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺; M³⁺ is atrivalent metal selected from the group consisting of Al³⁺, Fe³⁺, Cr³⁺,Co³⁺, and In³⁺; A^(n−) is an n-valence anion selected from the groupconsisting of OH⁻, F⁻, Cl⁻, Br⁻, NO₃ ⁻, CO₃ ²⁻, SO₄ ²⁻, Fe(CN)_(b) ³⁻,CH₃COO⁻, oxalate ion and salicylate ion; and x: 0<x≦0.33, ii) Acid clayor activated clay iii) Natural zeolite or artificial zeolite iv) Amixture of two or more members selected from the group consisting of thepreceding groups i)-iii).
 2. The spontaneous firing explosivecomposition as set forth in claim 1, wherein said binder is selectedfrom the group consisting of hydrotalcite having a formulaMg₆Al₂(OH)₁₆CO₃·4H₂O, pyroaurite having a formula ofMg₆Fe₂(OH)₁₆CO₃·4H₂O and a mixture thereof.
 3. The spontaneous firingexplosive composition as set forth in claim 1, wherein said fuel isaminotetrazole.
 4. The spontaneous firing explosive composition setforth in claim 1, wherein said combustion modifier is molybdenum or anoxide thereof.
 5. The spontaneous firing explosive composition as setforth in claim 1, wherein a 50% average particle diameter of a referencenumber of said potassium nitrate is 5-80 μm.
 6. The spontaneous firingexplosive composition as set forth in claim 1, wherein said combustionmodifier is present in an amount of 2-10% by weight.
 7. The spontaneousfiring explosive composition as set forth in claim 1, wherein a 50%average particle diameter of a reference number of said combustionmodifier is 10 μm or less.
 8. The spontaneous firing explosivecomposition as set forth in claim 1, wherein said explosive compositionis granulated.
 9. The spontaneous firing explosive composition as setforth in claim 1, wherein a spontaneous firing temperature of saidexplosive composition falls in the range of 150 to 180° C.
 10. Anenhancer comprising said spontaneous firing explosive composition as setforth in any one of claims 1 to
 9. 11. A gas generating agent comprisingsaid spontaneous firing explosive composition as set forth in any one ofclaims 1 to
 9. 12. A gas generator comprising said enhancer set forth inclaim
 10. 13. A gas generator for an air bag comprising said gasgenerating agent as set forth in claim
 11. 14. The gas generatorcomprising an enhancer and a gas generating agent comprising saidspontaneous firing explosive composition as set forth in any one ofclaims 1 or 9 wherein a composition of said enhancer is substantiallythe same composition as said gas generating agent.